MicrOmega is a near-IR hyperspectral microscope designed to characterize
in situ
the texture and composition of the surface materials of the Hayabusa2 target asteroid. MicrOmega is implemented within ...the MASCOT lander (Ho et al. in Space Sci. Rev.,
2016, this issue
, doi:10.1007/s11214-016-0251-6). The spectral range (0.99–3.65 μm) and the spectral sampling (
20
cm
−
1
) of MicrOmega have been chosen to allow the identification of most potential constituent minerals, ices and organics, within each 25 μm pixel of the
3.2
×
3.2
mm
2
FOV. Such an unprecedented characterization will (1) enable the identification of most major and minor phases, including the potential organic phases, and ascribe their mineralogical context, as a critical set of clues to decipher the origin and evolution of this primitive body, and (2) provide the ground truth for the orbital measurements as well as a reference for the analyses later performed on returned samples.
The OMEGA visible/near‐infrared imaging spectrometer on Mars Express has observed the retreat of the northern seasonal deposits during Martian year 27–28 from the period of maximum extension, close ...to the northern winter solstice, to the end of the retreat at Ls 95°. We present the temporal and spatial distributions of both CO2 and H2O ices and propose a scenario that describes the winter and spring evolution of the northern seasonal deposits. During winter, the CO2‐rich condensates are initially transparent and could be in slab form. A water ice annulus surrounds the sublimating CO2 ice, extending over 6° of latitude at Ls 320°, decreasing to 2° at Ls 350°, and gradually increasing to 4.5° at Ls 50°. This annulus first consists of thin frost as observed by the Viking Lander 2 and is then overlaid by H2O grains trapped in the CO2‐rich ice layer and released during CO2 sublimation. By Ls 50°, H2O ice spectrally dominates most of the deposits. In order to hide the still several tens of centimeters thick CO2 ice layer in central areas of the cap we propose the buildup of an optically thick top layer of H2O ice from ice grains previously embedded in the CO2 ice and by cold trapping of water vapor from the sublimating water ice annulus. The CO2 ice signature locally reappears between Ls 50° and 70°. What emerges from our observations is a very active surface‐atmosphere water cycle. These data provide additional constraints to the general circulation models simulating the Martian climate.
Key Points
How does the spatial distribution of seasonal ices evolve during their retreat?
How does the stratigraphy of seasonal deposits evolve during their retreat?
How intense is the surface‐atmosphere water cycle during northern spring?
The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) is a hyperspectral imager on the Mars Reconnaissance Orbiter (MRO) spacecraft. CRISM consists of three subassemblies, a gimbaled ...Optical Sensor Unit (OSU), a Data Processing Unit (DPU), and the Gimbal Motor Electronics (GME). CRISM's objectives are (1) to map the entire surface using a subset of bands to characterize crustal mineralogy, (2) to map the mineralogy of key areas at high spectral and spatial resolution, and (3) to measure spatial and seasonal variations in the atmosphere. These objectives are addressed using three major types of observations. In multispectral mapping mode, with the OSU pointed at planet nadir, data are collected at a subset of 72 wavelengths covering key mineralogic absorptions and binned to pixel footprints of 100 or 200 m/pixel. Nearly the entire planet can be mapped in this fashion. In targeted mode the OSU is scanned to remove most along‐track motion, and a region of interest is mapped at full spatial and spectral resolution (15–19 m/pixel, 362–3920 nm at 6.55 nm/channel). Ten additional abbreviated, spatially binned images are taken before and after the main image, providing an emission phase function (EPF) of the site for atmospheric study and correction of surface spectra for atmospheric effects. In atmospheric mode, only the EPF is acquired. Global grids of the resulting lower data volume observations are taken repeatedly throughout the Martian year to measure seasonal variations in atmospheric properties. Raw, calibrated, and map‐projected data are delivered to the community with a spectral library to aid in interpretation.
The Observatoire pour la$Min\acute{e}ralogie$, l'Eau, les Glaces, et$l'Activit\acute{e}$(OMEGA) visibleinfrared imaging spectrometer extensively observed regions of Mars with latitudes ...above$70\textdegree N$in late 2004 (heliocentric longitude from$L_s 93\textdegree to L_s 127\textdegree$). The extent of water ice at the surface and the size of ice grains were monitored as a function of time. Bright, small-grained frost, which initially covered a large fraction of the polar cap, waned in favor of large-grained ice. In outlying regions, dominated by large-grained ice, the albedo increased over the period. Evaluating the dust content was model dependent. However, contamination of ice by dust was low.
Aram Chaos is a crater 280 km in diameter centered at 2.5°N, 338.5°E. It is filled by chaotic terrains overlain by a dome‐shaped, layered 900 m thick formation displaying spectral signatures of ...ferric oxides on Thermal Emission Spectrometer (TES) and Observatoire pour la Mineralogie, L'Eau, les Glaces et L'Activite (OMEGA) medium spatial resolution data. We describe in detail the mineralogical composition, structure, and morphology of this crater fill using high‐resolution data (OMEGA, Mars Orbiter Laser Altimeter, Mars Orbiter Camera, TES, Thermal Emission Imaging System, and High‐Resolution Imaging Science Experiment). We infer the following formation scenario: the crater was first filled by a geological formation, the composition of which remains unclear because it is covered by dust. Widespread fracturing of this formation led to the development of chaotic terrains. Later, a second layered formation, presently dome shaped, was emplaced unconformably on the chaotic terrains. This younger unit is composed of a bright, poorly consolidated material that contains both monohydrated sulfates and ferric oxides according to OMEGA data. The surface of this formation is partially covered by dust and displays landforms indicating that the bright material has been mobilized by wind during or after its deposition. After its emplacement, this formation has been grooved down to various depths by large eolian erosion corridors. In these corridors, eolian removal of the bright material with a sulfate‐rich matrix has left debris fans, sand sheets, and dunes, which display some of the strongest spectral signatures of ferric oxides on Mars. Similar residual deposits enriched in ferric oxides, overlying a layered formation containing both ferric oxides and sulfates, have been observed by the Opportunity rover in Meridiani Planum, suggesting a common formation process.
The OMEGA visible/near‐infrared imaging spectrometer on board Mars Express has observed the southern seasonal cap in late 2004 and 2005 and then in the summer of 2006. These observations extended ...from the period of maximum extension, close to the southern winter solstice, to the end of the recession at Ls 325°. The spectral range and spectral resolution of OMEGA make it possible to monitor the extent and effective grain size of CO2 ice and H2O ice on the ground, the level of contamination of CO2 ice and H2O ice by dust, and the column density of μm‐sized ice grains in the atmosphere. The CO2 seasonal cap is very clean and clear in early southern winter. Contamination by H2O ice spreads eastward from the Hellas basin until the southern spring equinox. During southern spring and summer, there is a very complex evolution in terms of effective grain size of CO2 ice and contamination by dust or H2O ice. H2O ice does not play a significant role close to the southern summer solstice. Contamination of CO2 ice by H2O ice is only observed close to the end of the recession, as well as the few H2O ice patches already reported by Bibring et al. (2004a). These observations have been compared to the results of a general circulation model, with good qualitative agreement on the distribution of H2O ice on the surface and in the atmosphere. Resolving the remaining discrepancies will improve our understanding of the water cycle on Mars.
The East Candor Interior Layered Deposit (ILD) has signatures of mono‐ and polyhydrated sulfate in alternating layers that give insight into the processes which formed these layered deposits and on ...the environmental conditions acting on them since then. We use orbital data to explore multiple hypotheses for how these deposits formed: (1) sulfate‐bearing ILDs experience hydration changes on seasonal to a few years timescales under current Mars environmental conditions; (2) the deposits experience hydration under recent Mars conditions but require the wetter climate of high obliquity; and (3) the kieserite could be an original or diagenetic part of a complex evaporite mineral assemblage. Modeled climatology shows recent Mars environmental conditions might pass between multiple sulfate fields. However, comparison of Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité (OMEGA) and Compact Reconnaissance Imaging Spectrometer (CRISM) observations of the same ILD do not show changes in hydration over 2 Mars years. Low temperatures might slow the kinetics of that transition; it is likely that more clement conditions during periods of high obliquity are needed to overcome mineral metastability and hydrate kieserite‐bearing deposits. We find the alternate model, that the deposit is a cyclic evaporite sequence of mono‐ and polyhydrated sulfates, also plausible but with an unexplained dearth of Fe sulfates.
The MASCOT Camera (MasCam) is part of the Mobile Asteroid Surface Scout (MASCOT) lander’s science payload. MASCOT has been launched to asteroid (162173) Ryugu onboard JAXA’s Hayabusa 2 asteroid ...sample return mission on Dec 3rd, 2014. It is scheduled to arrive at Ryugu in 2018, and return samples to Earth by 2020. MasCam was designed and built by DLR’s Institute of Planetary Research, together with Airbus-DS Germany. The scientific goals of the MasCam investigation are to provide ground truth for the orbiter’s remote sensing observations, provide context for measurements by the other lander instruments (radiometer, spectrometer and magnetometer), the orbiter sampling experiment, and characterize the geological context, compositional variations and physical properties of the surface (e.g. rock and regolith particle size distributions). During daytime, clear filter images will be acquired. During night, illumination of the dark surface is performed by an LED array, equipped with
4
×
36
monochromatic light-emitting diodes (LEDs) working in four spectral bands. Color imaging will allow the identification of spectrally distinct surface units. Continued imaging during the surface mission phase and the acquisition of image series at different sun angles over the course of an asteroid day will contribute to the physical characterization of the surface and also allow the investigation of time-dependent processes and to determine the photometric properties of the regolith. The MasCam observations, combined with the MASCOT hyperspectral microscope (MMEGA) and radiometer (MARA) thermal observations, will cover a wide range of observational scales and serve as a strong tie point between Hayabusa 2’s remote-sensing scales (
10
3
–
10
−
3
m
) and sample scales (
10
−
3
–
10
−
6
m
). The descent sequence and the close-up images will reveal the surface features over a broad range of scales, allowing an assessment of the surface’s diversity and close the gap between the orbital observations and those made by the in-situ measurements. The MasCam is mounted inside the lander slightly tilted, such that the center of its 54.8° square field-of-view is directed towards the surface at an angle of 22° with respect to the surface plane. This is to ensure that both the surface close to the lander and the horizon are observable. The camera optics is designed according to the Scheimpflug principle, thus that the entire scene along the camera’s depth of field (150 mm to infinity) is in focus. The camera utilizes a
1024
×
1024
pixel CMOS sensor sensitive in the 400–1000 nm wavelength range, peaking at 600–700 nm. Together with the f-16 optics, this yields a nominal ground resolution of 150 micron/px at 150 mm distance (diffraction limited). The camera flight model has undergone standard radiometric and geometric calibration both at the component and system (lander) level. MasCam relies on the use of wavelet compression to maximize data return within stringent mission downlink limits. All calibration and flight data products will be generated and archived in the Planetary Data System in PDS image format.
This study presents the latest results on the mesospheric CO2 clouds in the martian atmosphere based on observations by OMEGA and HRSC onboard Mars Express. We have mapped the mesospheric CO2 clouds ...during nearly three martian years of OMEGA data yielding a cloud dataset of a1460 occurrences. The global mapping shows that the equatorial clouds are mainly observed in a distinct longitudinal corridor, at seasons L s =0-60A and again at and after L s =90A. A recent observation shows that the equatorial CO2 cloud season may start as early as at L s =330A. Three cases of mesospheric midlatitude autumn clouds have been observed. Two cloud shadow observations enabled the mapping of the cloud optical depth (Ie" =0.01-0.6 with median values of 0.13-0.2 at I' =1I14m) and the effective radii (mainly 1-3I14m with median values of 2.0-2.3I14m) of the cloud crystals. The HRSC dataset of 28 high-altitude cloud observations shows that the observed clouds reside mainly in the altitude range a1460-85km and their east-west speeds range from 15 to 107m/s. Two clouds at southern midlatitudes were observed at an altitude range of 53-62km. The speed of one of these southern midlatitude clouds was measured, and it exhibited west-east oriented speeds between 5 and 42m/s. The seasonal and geographical distribution as well as the observed altitudes are mostly in line with previous work. The LMD Mars Global Climate Model shows that at the cloud altitude range (65-85km) the temperatures exhibit significant daily variability (caused by the thermal tides) with the coldest temperatures towards the end of the afternoon. The GCM predicts the coldest temperatures of this altitude range and the season L s =0-30A in the longitudinal corridor where most of the cloud observations have been made. However, the model does not predict supersaturation, but the GCM-predicted winds are in fair agreement with the HRSC-measured cloud speeds. The clouds exhibit variable morphologies, but mainly cirrus-type, filamented clouds are observed (nearly all HRSC observations and most of OMEGA observations). In a1415% of OMEGA observations, clumpy, round cloud structures are observed, but very few clouds in the HRSC dataset show similar morphology. These observations of clumpy, cumuliform-type clouds raise questions on the possibility of mesospheric convection on Mars, and we discuss this hypothesis based on Convective Available Potential Energy calculations.
OMEGA/Mars Express has discovered large outcrops rich in phyllosilicates in the region of Mawrth Vallis, Mars (around 20°W, 25°N). The region is located in Noachian highly cratered terrains, close to ...the limit of the Martian dichotomy, where the outflow channel Mawrth Vallis cuts the highlands. We have examined this region using OMEGA spectra of the surface from 0.9 μm to 2.6 μm, with spatial sampling from 500 m to 3 km, offering a full coverage of the region. OMEGA spectra show two broad bands centered at 1 μm and 2.2 μm, revealing the presence of clinopyroxene on dark surfaces. Phyllosilicates have been identified by absorption bands at 1.4 μm, 1.9 μm, and 2.2 or 2.3 μm. Comparison with laboratory spectra reveals similarities with Al‐OH smectites such as montmorillonites, or Fe‐ or Mg‐OH smectites such as nontronite. A precise location of the phyllosilicate‐rich areas on visible HRSC images indicates that they are placed exclusively on bright outcrops, mostly on the plateaus, dated to the Noachian period. On HRSC and MOC images the phyllosilicate‐rich outcrops reveal strong erosional features such as numerous residual buttes composed of layers a few meters thick. The phyllosilicate‐rich unit corresponds to a geological unit more than 100 m thick, over a horizontal extension approximately of 300 km × 400 km. This unit implies a large volume of altered rocks, either in situ or after transport and deposition, in Noachian terrains, revealing a different climatic and geologic environment from the present one.
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